Two mobile phone dynasties in trouble: Nokia and Microsoft. Nokia has binned its chief executive, and seen the head of its mobile phone business decide that he doesn't want to hang around after not getting the job. Microsoft, meanwhile, has seen its Windows Mobile brand ground into the dust, first by the iPhone and then by Google's Android. Even worse, its Kin phone - the outcome of its $500m acquisition of the very popular Danger phone maker - died on its feet, and was withdrawn after only a few weeks on sale from US carrier Verizon; it hasn't made it over to Europe.

Now they're back, with new phones, new looks.

It's self-evident that what makes smartphone effective is its software - the operating system, the inbuilt apps, and the developer ecosystem. Quite often, the surface matters; it's no good having a fantastic operating system under the hood if it's impossible to get anything done without resorting to hard-to-memorise incantations. That's why most of us use windowing systems rather than command lines. Equally, if you have a windowing system on a touch-screen system, you need one which is consistent and responsive and informative: if touching an app sometimes does one thing and other times something else, that's no good; ditto if the same app looks different in different places but does the same thing, or if the display doesn't tell you what's going on.

With that in mind, here are my potted analyses of Nokia's latest phones (using Symbian S^3), and separately of Windows Phone 7, from a user interface perspective.

Nokia

If I were to choose one word to describe the S^3 interface on the N8/E7/C6/C7, it would be: inconsistent. If I had another word to throw in, it would be sluggish.

There's a lack of consistency in the hardware design, which contrasts heavily with Windows Phone 7, where there will always be three, and just three, main buttons on the bottom edge of the phone: Back, Home, and Search.

On the Nokia phones, the home button wanders all over: on the E7 there's a single button in the middle; on the N8, it's on the bottom left; on the C7, there's a green button on the left, a black one in the middle, and a red one on the right. Why? Why not have it in a standard place, so each Nokia smartphone is consistent?

That reminds me of Apple in the mid-90s, before Jobs returned and shook it by the scruff of the neck: there were loads of different products, and as Don Norman, a user interface expert who worked there recalls, there wasn't even consistency in where you'd find the power button. That led to horrendous supply chain and manufacturing problems and pushed up costs unnecessarily (because you couldn't use surplus buttons from another low-selling range if you were short of those for a high-selling range).

Next, the interface. The S^3 interface has a number of problems with consistency and the message it gives you. For instance, the first screen when the phone is turned on has a number of translucent icons; you can see some of the background image through them. Swiping to the right or left pulls up another screen, but there was a definite lag - so bad that by swiping back and forth quickly you can put the system into hysteresis - you're swiping to the right but the screen is still moving to the left. That's terrible UI design. And this was on the demonstration phones, which aren't encumbered with extras.

Sure, you can say that nobody's going to do that. But swiping is a fundamental behaviour of the phone; if it can't handle this, then that promises badly for other UI interactions. Can you imagine Steve Jobs ever allowing an iPhone with such a flaw out of the door? I've got a two-year-old iPod Touch, which creaks along on the new iOS 4.01 (loading apps takes an age), but I can't get that hysteresis to happen.

There are other elements which betray a lack of integrated design. The initial screen on these phones show a number of translucent icons (you can change which ones); some of the background image is visible through them. Press an icon and it launches that app. Fair enough. Next, try a swipe to the right (which is what the iPhone and Android interfaces have made the default): you get a new screen. However, it's not got the same background image as the previous one - because, it turns out, that "front" page is an app - the menu - and now you're looking at the list of apps. But (another UI flaw) you might not realise that you've got a lot of apps, because you only get a scroll bar on the right-hand side of the display once you start scrolling.

And why have a separate folder of apps? Why shouldn't the apps be directly accessible from the menu? (And why is the menu a separate app in its own right? Conceptually, that's very strange.) Once you start asking questions like this, you get pulled down a rabbit hole of wondering quite who had the overall vision of how the software should be designed, and whether they tested it for irritancy on humans.

The E7 also has a slide-out keyboard (which Nokia board member Niklas Savander memorably struggled, and failed, to slide out and demonstrate when I met him). It's surprisingly hard to get out; you have to know where to prod, or how to pull, and there are no immediately obvious clues. Very likely you would know within a week of using it, but intuitive design - as Norman puts it, the "affordances" of an object (such as handles or knobs on doors) - should communicate itself at once.

Personally, I didn't like the keyboard - not for the button action, but for its width/height ratio: compared to a BlackBerry, G1 Android (the first slide-out keyboard model) or iPhone, the E7's keyboard is extremely wide and not very high, which means your thumbs are moving around a lot yet struggling to find keys. A less wide keyboard would have been better. It would be interesting to know what user testing Nokia did on this, and especially what comparative testing it did against its own existing phone range and other smartphones. (Nokia people, you can contact me. Anonymity guaranteed.)

Overall? I was surprised by the low quality. The hardware on these phones may be stunning, but if basic things like screen swipes don't work correctly, there's always going to be an annoyance factor.